Unlocking the door for synergizing expansion-capacity in Si anodes: breathable flexible MOFs

The trade-off dilemma between volume expansion and capacity limits the application of Si-based anodes in Li-ion batteries. Breathable flexible metal-organic frameworks (MOFs) provide a viable strategy to tackle this challenge. They can relieve lithiation-induced mechanical stress via reversible coordination deformation of metal nodes and organic ligands, while maximizing the retention of specific capacity. This review first elaborates the lithium storage mechanism of silicon and compares traditional volume suppression strategies, proving excessive expansion inhibition inevitably sacrifices specific capacity. MOF modifiers are divided into breathable flexible MOFs, rigid MOFs and MOF-derived carbons, and their differentiated mechanisms for mitigating volume expansion and stabilizing SEI films are comprehensively elucidated. Four core preparation optimization strategies including conductivity compensation, interfacial bonding reinforcement, ligand engineering, crystal engineering are summarized. Major bottlenecks such as unclear node-ligand matching rules, high manufacturing cost, low volumetric energy density and insufficient quantitative characterization of MOF breathing behavior are outlined. Corresponding research priorities covering quantitative structure-property correlation, non-destructive encapsulation and in situ dynamic characterization are put forward. This review provides a theoretical basis and technical guidance for the scalable application of high-performance silicon anodes in LIBs.