Deciphering the dual functions of a silicon dioxide protective layer in regulating lithium-ion deposition

Abstract

Silicon dioxide (SiO₂) is widely applied as a protective layer of lithium (Li) metal, as it can suppress the growth of Li dendrites and prolong cycling life. However, fundamental understanding of how the SiO₂ protective layer affects Li-ion deposition behavior is still limited. Such knowledge would be very desirable for the practical use of Li metal. Herein, a systematic study investigating the role of SiO₂ as a protective layer for realizing uniform Li-ion deposition is described. Based on the successful construction of model materials, it was found that the SiO₂ protective layer offers dual functions in improving Li deposition behaviors. The SiO₂ protective layer can assist in the rapid transfer of Li ions from the electrolyte to the Li metal surface, while SiO₂ near the Li metal surface can be used as lithiophilic sites to guide Li nucleation. Consequently, Li metal protected by SiO₂ favors homogeneous Li nucleation/growth and successfully inhibits the formation of dendrites during prolonged cycling. An impressive long cycling stability for over 400 h with a low potential hysteresis was obtained in a symmetrical cell with protected Li, and an extended cycling life was achieved for protected Li when coupled with LiNi_0.5Co_0.2Mn_0.3O₂ cathode.