Insight into the formation and stability of solid electrolyte interphase (SEI) for nanostructured silicon-based anode electrodes used in Li-ion batteries
Silicon-based anode fabrication with nano-scale structuration improves the energy density and life cycle of Li-ion batteries. As-synthesized silicon (Si) nanowires (NWs) or nanoparticles (NPs) directly on the current collector represent a credible alternative to conventional graphite anode. However, the operating potentials of these electrodes are below the electrochemical stability window of all electrolytes used in commercial Li-ion systems. During the first charging phase of the cell, partial decomposition of the electrolyte takes place, which leads to the formation of a layer at the surface of the electrode, called Solid Electrolyte Interphase (SEI). A stable and continuous SEI layer formation is a critical factor to achieve reliable life-time stability of the battery. Once formed, the SEI acts as a passivation layer that minimizes further degradation of the electrolyte during cycling, while allowing lithium ions diffusion with their subsequent insertion into the active material and ensures reversible operation of the electrode. However, one of the major issues requiring deeper investigation is the assessment of the morphological extension of the SEI layer into the active material which is one of the main parameters affecting the anode performances. In the present study, we use electron tomography (ET) with low electron dose to retrieve three-dimensional information on the SEI layer formation and its stability around SiNWs and SiNPs. The possible mechanisms of the SEI evolution could be inferred from the interpretation and analysis of the reconstructed volumes. Significant volume variations in the SiNW and an inhomogeneous distribution of the SEI layer around the NWs are observed during cycling and provide insights of the potential mechanism leading to the generally reported SiNWs anodes capacity fading. By contrast, analysis of the reconstructed SiNPs’ volume for a sample undergoing one lithiation-delithiation cycle evidence that the SEI remains homogeneously distributed around the NPs that retain their spherical morphology and points to the potential benefit of such nanoscale Si anode materials to improve their cycling lifetime.
This work received financial support from Chaire EDF “Energies Durable”, the French state managed by the National Research Agency under the Investments for the Future program under the references ANR-10-EQPX-50 pole NanoMax & &NanoTEM. For the tomography studies, the authors acknowledge financial support from the CNRS and CEA METSA electron microscopy network (FR3507). IF and LL would like to thank Sergio Marco for the Cryogenic sample holder used for the 2D-TEM preliminary experiments. Lucian Roiban is gratefully acknowledged for fruitful discussions. The authors would also like to acknowledge the Centre Interdisciplinaire de Microscopie électronique de l’X (CIMEX). This work is part of the NanoMaDe-3E Initiative
(M. Ezzedine et al.: https://doi.org/10.1021/acsami.1c03302)