Borderline Metal Centers on Nonporous Metal‐Organic Framework Nanowire Boost Fast Li‐Ion Interfacial Transport of Composite Polymer Electrolyte

Metal-organic frameworks (MOFs) fillers are emerging for composite polymer electrolytes (CPEs). Enhancing Lewis acid-base interaction (LABI) among MOFs, polymer and Li-salt is expected to promote Li+ -transport. However, it is unclear how to customize a strong LABI interface. The large surface-area of classical MOFs also interferes with clarifying the LABI influence on Li+ -transport. Herein, Bi3+ as metal centers to design colloidal-dispersed nonporous MOFs (Bi/HMT-MOFs) nanowire with a surface-area of only 17.13 m2 g-1 to prepare polyethylene oxide (PEO)-based CPEs (BMCPE) is chosen. The nonporous feature can exclude the surface-area effect on Li+ -transport. More interestingly, Bi3+ is a typical borderline acid, which can interact with both hard-basic PEO and soft-basic Li-salt anion. Accordingly, Bi/HMT-MOFs are uniformly dispersed in the BMCPE to form a strong LABI interface with PEO and Li-salt, promoting Li-salt dissociation and providing rapid Li+ -transport channels. Despite the ultralow surface-area of Bi/HMT-MOFs, BMCPE exhibits significantly enhanced ion-conductivity and Li+ transference number, which completely rival traditional MOFs-filled CPEs. BMCPE also enables symmetric and full cells with excellent high-rate performance and long-term cycling stability. In contrast, when Bi3+ sites are obscured, electrochemical performances are obviously decreased. Therefore, employing borderline metal centers will be an effective strategy to construct a LABI interface for high-performance MOFs-filled CPEs.