Lithium-ion batteries have received significant research interest due to their advantages in energy and power density, which are important to enabling many devices. One route to further increase energy density is to fabricate thicker electrodes in the battery cell; however, careful consideration must be taken when designing electrodes as to how increasing the thickness impacts the multiscale and multiphase molecular transport processes, which can limit the overall battery operating power. Design of these electrodes necessitates probing the molecular processes when the battery cell undergoes electrochemical charge/discharge. One tool for in situ insights into the cell is neutron imaging, because neutron imaging can provide information of where electrochemical processes occur within the electrodes. In this manuscript, neutron imaging is applied to track the lithiation/delithiation processes within electrodes at different current densities for a full cell with a thick sintered Li₄Ti₅O₁₂ anode and LiCoO₂ cathode. The neutron imaging reveals that the molecular distribution of Li⁺ during discharge within the electrode is sensitive to the current density, or equivalently discharge rate. An electrochemical model provides additional insights into the limiting processes occurring within the electrodes. In particular, the impact of tortuosity and molecular transport in the liquid phase within the interstitial regions in the electrodes are considered, and the influence of tortuosity was shown to be highly sensitive to the current density. Qualitatively, the experimental results suggest that the electrodes behave consistent with the packed hard sphere approximation of Bruggeman tortuosity scaling, which indicates that the electrodes are largely mechanically intact but also that a design that incorporates tunable tortuosity could improve the performance of these types of electrodes.

中文翻译：

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用中子成像探测厚烧结电池电极的传输限制

锂离子电池因其在能量和功率密度方面的优势而受到了极大的研究兴趣，这对于启用许多设备很重要。进一步提高能量密度的一种方法是在电池单元中制造更厚的电极。然而，在设计电极时必须仔细考虑增加厚度如何影响多尺度和多相分子传输过程，这可能会限制电池的整体运行功率。当电池进行电化学充电/放电时，这些电极的设计需要探索分子过程。一种原位工具对电池的深入了解是中子成像，因为中子成像可以提供有关电极内发生电化学过程的位置的信息。在这篇手稿中，中子成像用于跟踪具有厚烧结 Li ₄ Ti ₅ O ₁₂阳极和 LiCoO ₂阴极的全电池在不同电流密度下电极内的锂化/脱锂过程。中子成像揭示了 Li ⁺的分子分布在放电过程中，电极内的电流密度或等效放电率是敏感的。电化学模型为电极内发生的限制过程提供了额外的见解。特别是，考虑了电极间隙区域内液相中曲折度和分子传输的影响，曲折度的影响对电流密度高度敏感。定性地，实验结果表明电极的行为与 Bruggeman 曲折度缩放的填充硬球近似一致，这表明电极在很大程度上是机械完整的，但包含可调曲折度的设计可以提高这些类型的电极的性能。