Interfacial degradation of silicon anodes in pouch cells

The practical application of silicon (Si) anodes in the next-generation high-energy lithium-ion batteries (LIBs) is largely hindered by their capacity loss due to the formation of a solid electrolyte interphase (SEI). Although much work has been carried out to investigate the interfacial evolution of Si, most of them focused on nanostructured Si cycled in coin cells or customer-designed cells, whose working conditions are far from practical usage. Herein, the capacity degradation mechanism and associated interfacial evolution of the micro-sized Si particles cycled in pouch cells are uncovered through multi-scale imaging and spectroscopy techniques, especially cryogenic electron microscopy (cryo-EM). The results show that the surface of Si particles is gradually corroded by the electrolyte, forming a thick (up to 2.5 μm after 300 cycles) and porous SEI rich in organic carbonates and Li_xSiO_y. After profiling the nanostructure and chemical distribution across it, the porosity of the SEI is determined to be ∼53.5% and thus a bottom-up SEI growth mechanism is proposed. To achieve a dense and stable SEI, an elastic SEI with a crosslinking network is used to enhance the interfacial stability of the Si anode. Our findings not only reveal the underlying failure mechanism of the Si anode beneficial for its practical applications but also provide a comprehensive understanding of dynamic interfacial evolution enlightening for future interfacial design to achieve high-performance batteries.