General Strategy To Synthesize Highly Dense Metal Oxide Quantum Dots-Anchored Nitrogen-Rich Graphene Compact Monoliths To Enable Fast and High-Stability Volumetric Lithium/Sodium Storage

Volumetric performance of a material is more attractive than gravimetric performance in consumer electronics and electric vehicles but rarely emphasized in earlier studies of lithium-ion batteries (LIBs), especially current sodium-ion batteries (SIBs). Herein, we report a simple and general strategy with the assistance of a small amount of graphene oxide (similar to 10 wt %) as an "assembled binder" to design porous yet highly dense metal oxide quantum dots-anchored nitrogen-rich reduced graphene oxide (denoted as HD-MOx-N-RGO) compact monoliths. By taking TiO2 as a representative, the as-fabricated HD-TiO2-N-RGO compact monolith, consisting of well-dispersed and ultrasmall-sized TiO2 quantum dots (similar to 4.0 nm) anchored on N-RGO, exhibits a high electrical conductivity of 343.7 S m(-1), high density of 1.8 g cm(-3), and porosity, thus both leading to high gravimetric and volumetric capacities without degradation after 100 cycles at 0.1 A g(-1) and superior rate capability at 10 or 5 A g(-1) as anode in LIBs and SIBs, respectively. More importantly, when the current density is increased to 2.0 A g(-1), it still both exhibits a high-stability lifespan with over 91% capacity retention after 1000 cycles in LIBs and SIBs. Detailed analysis of microstructures, composition, and electrochemical kinetics reveal that the superior rate and long-cycling performance stem from the ultrasmall size of TiO2-QDs and the strong interaction between N-RGO and TiO2, which not only facilitates bulk Li+/Na+ intercalation, but also improves the interfacial Li/Na storage. This study demonstrates our strategy is very promising in designing compact energy storage materials with fast and high-stability volumetric performance.