Structure and composition of silicon microarrays subjected to cyclic insertion and extraction of lithium

Abstract

The silicon anodes for lithium-ion batteries subjected to cyclic tests of variable duration are studied by electron microscopy, energy-dispersive X-ray analysis, and Raman scattering. It is shown that the discharge capacity of electrodes based on macroporous silicon degrade due to the fracture of silicon walls and the formation of a Si-Li amorphous phase. Both effects arise early on testing. The number of cracks and the degree of disorder of the silicon crystal lattice are found to grow with the number of lithiation cycles and be nonuniformly distributed along the height of the walls. Namely, lithium is incorporated largely into the upper part of the structure adjacent to the separator. The disorder degree of the crystal lattice in the lithiated anodes is compared with that in standard amorphous silicon by analysis of the Raman spectra.