High void space utilization of yolk-shell structured silicon anodes achieved via water-etching strategy

Silicon, as a promising candidate for anode materials of next-generation lithium-ion batteries with high energy density, has suffered from severe capacity degradation and unstable solid electrolyte interface induced by the huge volume change during cycling. Employing yolk-shell design has been demonstrated as an effective strategy to alleviate this issue by incorporating void spaces and an electrolyte blocking layer into the structure. However, introduction of void spaces inevitably reduces the volumetric capacity of Si anodes. Herein, a rational yolk-shell structure with tailored void spaces targeting the expansion behaviors of polycrystalline silicon has been designed that achieved high void space utilization upon lithiation via a novel water-etching approach. Uniform and well-defined void spaces were formed in the one-step water etching process that accommodated the quasi-isotropic expansion of polycrystalline silicon nanoparticles with minimal redundant void spaces. The yolk-shell structure remained intact during cycling that enabled a stable solid electrolyte interface to be formed on the conformal double-walled shell. Such engineered yolk-shell endowed the Si-based anodes with maximized void space utilization and constant structural integrity, delivered a high volumetric capacity (1773 mAh cm–3), an outstanding cycling stability (capacity retention of 90.4% after 1000 cycles), and a remarkable coulombic efficiency (99.88%).