Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853.
School of Applied and Engineering Physics, Cornell University, Ithaca, NY 14853.
Proc Natl Acad Sci U S A. 2023 Feb 14;120(7):e2220419120. doi: 10.1073/pnas.2220419120. Epub 2023 Feb 7.
The growing demands for high-energy density electrical energy storage devices stimulate the coupling of conversion-type cathodes and lithium (Li) metal anodes. While promising, the use of these "Li-free" cathodes brings new challenges to the Li anode interface, as Li needs to be dissolved first during cell operation. In this study, we have achieved a direct visualization and comprehensive analysis of the dynamic evolution of the Li interface. The critical metrics of the interfacial resistance, Li growth, and solid electrolyte interface (SEI) distribution during the initial dissolution/deposition processes were systematically investigated by employing multidimensional analysis methods. They include three-electrode impedance tests, in situ atomic force microscopy, scanning electrochemical microscopy, and cryogenic scanning transmission electron microscopy. The high-resolution imaging and real-time observations show that a loose, diffuse, and unevenly distributed SEI is formed during the initial dissolution process. This leads to the dramatically fast growth of Li during the subsequent deposition, deviating from Fick's law, which exacerbates the interfacial impedance. The compactness of the interfacial structure and enrichment of electrolyte species at the surface during the initial deposition play critical roles in the long-term stability of Li anodes, as revealed by operando confocal Raman spectroscopic mapping. Our observations relate to ion transfer, morphological and structural evolution, and Li (de)solvation at Li interfaces, revealing the underlying pathways influenced by the initial dissolution process, which promotes a reconsideration of anode investigations and effective protection strategies.
对高能量密度储能器件的需求不断增长，刺激了转换型阴极与锂（Li）金属阳极的耦合。虽然这种方法具有广阔的应用前景，但这些“无 Li”阴极的使用给 Li 阳极界面带来了新的挑战，因为在电池运行过程中，Li 需要首先溶解。在本研究中，我们实现了对 Li 界面动态演化的直接可视化和全面分析。通过采用多维分析方法，系统研究了初始溶解/沉积过程中界面电阻、Li 生长和固体电解质界面（SEI）分布的关键指标。这些方法包括三电极阻抗测试、原位原子力显微镜、扫描电化学显微镜和低温扫描透射电子显微镜。高分辨率成像和实时观察表明，在初始溶解过程中会形成疏松、弥散且分布不均匀的 SEI。这导致随后沉积过程中 Li 的快速生长，偏离了菲克定律，从而加剧了界面阻抗。在初始沉积过程中，界面结构的紧密程度和表面电解质物种的富集对 Li 阳极的长期稳定性起着至关重要的作用，这一点通过在位共聚焦拉曼光谱映射得到了揭示。我们的观察结果涉及离子迁移、形态和结构演化以及 Li 在界面处的（脱）溶剂化，揭示了受初始溶解过程影响的潜在途径，这促使我们重新考虑对阳极的研究和有效的保护策略。
