A Lithium Ion Highway by Surface Coordination Polymerization: In Situ Growth of Metal-Organic Framework Thin Layers on Metal Oxides for Exceptional Rate and Cycling Performance

A thin layer of a highly porous metal-organic framework material, ZIF-8, is fabricated uniformly on the surface of nanostructured transition metal oxides (ZnO nanoflakes and MnO₂ nanorods) to boost the transfer of lithium ions. The novel design and uniform microstructure of the MOF-coated TMOs (ZIF-8@TMOs) exhibit dramatically enhanced rate and cycling performance comparing to their pristine counterparts. The capacities of ZIF-8@ZnO (nanoflakes) and ZIF-8@MnO₂ (nanorods) are 28 % and 31 % higher that of the pristine ones at the same current density. The nanorods of ZIF-8@MnO₂ show a capacity of 1067 mAh g^-1 after 500 cycles at 1 Ag^-1 and without any fading. To further improve the conductivity and capacity, the ZIF-8-coated materials are pyrolyzed at 700 °C in an N₂ atmosphere (ZIF-8@TMO-700 N). After pyrolysis, a much higher capacity improvement is achieved: ZIF-8@ZnO-700 N and ZIF-8@MnO₂ -700 N have 54 % and 69 % capacity increases compared with the pristine TMOs, and at 1 Ag^-1 , the capacity of ZIF-8@MnO₂ -700 N is 1060 mAh g^-1 after cycling for 300 cycles.