Hierarchically Porous Silica Membrane as Separator for High-Performance Lithium-Ion Batteries

Commercial polymeric separators in lithium-ion batteries (LIBs) typically suffer from limited porosity, low electrolyte wettability, and poor thermal and mechanical stability, which can degrade the battery performance especially at high current densities. Here, the design of hierarchically porous, ultralight silica membranes as separator for high-performance LIBs is reported through the assembly of hollow mesoporous silica (HMS) particles on the cathode surface. The rich mesopores and large cavity of individual HMS particles provide low-tortuosity pathways for ionic transport, while simultaneously serving as electrolyte reservoir to further boost the electrochemical kinetics. Moreover, benefiting from their inorganic and hierarchically porous nature, such HMS separators display better electrolyte affinity, thermal stability, and mechanical strength than commercial polypropylene (PP) separators. As a demonstration, LIBs with a LiFePO4 cathode coated with HMS separators exhibit exceptional rate capability and cycling stability, outperforming LIBs with PP and Al2O3-modified PP separators as well as separators made of solid silica particles.