Facile Universal Mass Production Strategy to Sub-3 nm Monodisperse Nanocrystals of Transition-Metal Oxides and Their Excellent Cyclability for Li-Ion Storage

Nanoparticles, especially ultrasmall ones in sub-3 nm realms, are fundamental to high activity, high efficiency, and high utilization (3-H) important for many fields. Meanwhile, controlling the crystallinity, surfaces/interfaces, and pores, especially dimension-tunable aspect in them, is also of great significance in synthetic chemistry and nanoengineering. However, controlling crystallization down to a scale of sub-3 nm in mass production, even of subnucleus scale, is rare and still challenging. Here, using Mn, Co, and Zn elements as examples, homogeneous subnuclei smaller than 1 nm and size-tunable sub-3 nm monodisperse nanocrystals have been realized in laminated transition-metal oxides bulk foams (TMOBFs) of gram scale by a two-step fast evaporation-solidification (FE-S) and annealing strategy. Realization of the challenging size controllability in ultrasmall nanocrystals benefits from the FE-S-related burst nucleation process and in situ inhibition of crystal growth, while formation of the nanosheet skeletons is impelled by multiscale bubbling effect. Relying on annealing temperature and durations, the involved TMOBFs also exhibit controllable inorganic crystallization, organic surface/interfaces, and abundant micro/mesopores. In an illustration of the proof-of-concept application, TMOBFs with sub-3 nm nanocrystals substantiate universally ultrasteady cycling performance and approximate 100% utilization efficiency as anodes materials for lithium-ion batteries as expected.