Bifunctional MOFs with robust mesoporous armors and superionic conduction

Metal-organic frameworks (MOFs) have raised extensive attention for ionic conduction; however, the inferior ionic conductivity and weak mechanical strength of semi-solid MOF electrolytes have limited their further development. Here, bifunctional MOFs (BF-MOFs) with a yolk-shell structure have been designed to realize superionic conduction and high mechanical stiffness. In the BF-MOFs, the mesoporous shells work as robust armors for suppressing dendrite growth, and simultaneously provide perfect pathways for rapid and uniform ionic transport; the large gaps between the mesoporous shells and the MOF cores can store more Li ions for superionic conduction. In addition, the MOF cores function as ionic rectifiers for uniform Li deposition. As a result, the electrolyte with BF-MOFs delivers a high ionic conductivity of 1.27 × 10-3 S cm−1 at 30 °C and a high Li+ transference number of 0.74. An ultralong life of 4500 cycles with capacity retention of 96.5% is obtained in LiFePO4//Li cells. Furthermore, LiNi0.8Co0.1Mn0.1O2//Li cells are also fabricated, displaying remarkable durability with capacity retention of 92.2% after 800 cycles.