Integration of Highly Graphitic Three-Dimensionally Ordered Macroporous Carbon Microspheres with Hollow Metal Oxide Nanospheres for Ultrafast and Durable Lithium-Ion Storage

Achieving excellent electrochemical performance at high charging rate has been a long-cherished dream in the field of lithium-ion batteries (LIBs). As a part of the efforts to meet the goal, an innovative strategy for the synthesis of 3D porous highly graphitic carbon microspheres, to which numerous hollow metal oxide nanospheres are anchored, for use as anode in LIBs is introduced. Hollow carbon nanosphere-aggregated microspheres prepared from the spray drying process are graphitized with the aid of metal catalysts, and subsequent oxidation selectively removed amorphous carbon, leading to the formation of highly conductive graphitic carbon matrix. Numerous hollow metal oxide nanospheres formed simultaneously during the oxidation process via nanoscale Kirkendall diffusion are anchored onto the carbonaceous matrix, effectively reinforcing the structural integrity by alleviating volume changes and reducing lithium-ion diffusion lengths. The synergistic effect of combining hollow metal oxide nanospheres with high theoretical capacity with conductive carbon matrix led to accelerated electrochemical kinetics, resulting in high capacity at high charging rate. In addition, trapping the hollow metal oxide nanospheres inside hollow carbon nanospheres could effectively alleviate the volume changes, which led to high structural stability. When applied as LIB anodes, the microspheres exhibit a capacity of 411 mA h g-1 after 2500 cycles at 10.0 A g-1, with 80% capacity retention. The anode exhibits a high capacity of 274 mA h g-1 at an extremely high current density of 50.0 A g-1, thus demonstrating the structural merits of the microspheres.