Ultrafast Discharge/Charge Rate and Robust Cycle Life for High-Performance Energy Storage Using Ultrafine Nanocrystals on the Binder-Free Porous Graphene Foam

A hierarchical architecture fabricated by integrating ultrafine titanium dioxide (TiO2) nanocrystals with the binder-free macroporous graphene (PG) network foam for high-performance energy storage is demonstrated, where mesoporous open channels connected to the PG facilitate rapid ionic transfer during the Li-ion insertion/extraction process. Moreover, the binder-free conductive PG network in direct contact with a current collector provides ultrafast electronic transfer. This structure leads to unprecedented cycle stability, with the capacity preserved with nearly 100% Coulombic efficiency over 10 000 Li-ion insertion/extraction cycles. Moreover, it is proven to be very stable while cycling 10 to 100-fold longer compared to typical electrode structures for batteries. This facilitates ultrafast charge/discharge rate capability even at a high current rate giving a very short charge/discharge time of 40 s. Density functional theory calculations also clarify that Li ions migrate into the TiO2-PG interface then stabilizing its binder-free interface and that the Li ion diffusion occurs via a concerted mechanism, thus resulting in the ultrafast discharge/charge rate capability of the Li ions into ultrafine nanocrystals.