Shell-Protective Secondary Silicon Nanostructures\nas Pressure-Resistant High-Volumetric-Capacity Anodes for Lithium-Ion\nBatteries

Abstract

The\nnanostructure design of a prereserved hollow space to accommodate\n300% volume change of silicon anodes has created exciting promises\nfor high-energy batteries. However, challenges with weak mechanical\nstability during the calendering process of electrode fabrication\nand poor volumetric energy density remain to be solved. Here we fabricated\na pressure-resistant silicon structure by designing a dense silicon\nshell coating on secondary micrometer particles, each consisting of\nmany silicon nanoparticles. The silicon skin layer significantly improves\nmechanical stability, while the inner porous structure efficiently\naccommodates the volume expansion. Such a structure can resist a high\npressure of over 100 MPa and is well-maintained after the calendering\nprocess, demonstrating a high volumetric capacity of 2041 mAh cm^–3. In addition, the dense silicon shell decreases the\nsurface area and thus increases the initial Coulombic efficiency.\nWith further encapsulation with a graphene cage, which allows the\nsilicon core to expand within the cage while retaining electrical\ncontact, the silicon hollow structure exhibits a high initial Coulombic\nefficiency and fast rise of later Coulombic efficiencies to >99.5%\nand superior stability in a full-cell battery.