Fabrication of three-dimensionally interconnected nanoparticle superlattices and their lithium-ion storage properties

Abstract

Three-dimensional superlattices consisting of nanoparticles represent a new class of condensed materials with collective properties arising from coupling interactions between close-packed nanoparticles. Despite recent advances in self-assembly of nanoparticle superlattices, the constituent materials have been limited to those that are attainable as monodisperse nanoparticles. In addition, self-assembled nanoparticle superlattices are generally weakly coupled due to the surface-coating ligands. Here we report the fabrication of three-dimensionally interconnected nanoparticle superlattices with face-centered cubic symmetry without the presynthesis of the constituent nanoparticles. We show that mesoporous carbon frameworks derived from self-assembled supercrystals can be used as a robust matrix for the growth of nanoparticle superlattices with diverse compositions. The resulting interconnected nanoparticle superlattices embedded in a carbon matrix are particularly suitable for energy storage applications. We demonstrate this by incorporating tin oxide nanoparticle superlattices as anode materials for lithium-ion batteries, and the resulting electrochemical performance is attributable to their unique architectures.

Figure 1. Fabrication of three-dimensionally interconnected NP superlattices from mesoporous carbon frameworks.

(a) Schematic illustration of the fabrication procedure (cross-sectional view). (b,c) SEM and HRSEM images of carbonized Fe₃O₄ NP supercrystals, respectively. Scale bars, 1 μm and 200 nm, respectively. (d) SAXS patterns of carbonized Fe₃O₄ NP supercrystals and mesoporous carbon frameworks, respectively. (e,f) TEM images of mesoporous carbon frameworks with different lattice projections. Scale bars, 50 and 20 nm, respectively. The inset in (e) is a low-magnification SEM image of mesoporous carbon frameworks. Scale bar, 1 μm. The red arrows in (f) indicate the interconnected windows. (g) N₂ adsorption–desorption isotherms and the corresponding pore size distribution (inset) of mesoporous carbon frameworks. The red arrow indicates the small pores corresponding to the interconnected windows observed in (f).

Figure 2. Representative electron microscopy images of various NP superlattices.

(a) SEM image of SiO₂ NP superlattices, showing the faceted morphology. Scale bar, 500 nm. (b) HRSEM image of SiO₂ NP superlattices, showing the surface terraces and long-range NP ordering. Scale bar, 100 nm. (c,d) SEM and TEM images of 3D carbon NP superlattices, respectively. Scale bars, 100 and 50 nm, respectively.

Figure 3. Structural characterization of SnO₂ NP superlattices.

(a) TEM image of SnO₂ NP superlattices. Scale bar, 20 nm. (b,c) SAXS pattern and XRD pattern of SnO₂ NP superlattices, respectively. (d) HRTEM image of SnO₂ NP superlattices, showing the high crystallinity of the embedded SnO₂ NPs. Scale bar, 5 nm. The red arrows indicate NP interconnections.

Figure 4. Electrochemical characterization of SnO₂ NP superlattices.

(a) Representative cyclic voltammograms at a scan rate of 0.5 mV s⁻¹. (b) Cycling performance at a current density of 600 mA g⁻¹ and the corresponding Coulombic efficiency. The cycling performance of 13-nm SnO₂ NPs with and without carbon coating as well as carbon frameworks tested under the same conditions are also included for comparison. (c) Rate-capability test at current densities ranging from 120 to 3,000 mA g⁻¹. (d) TEM image and (e,f) the corresponding EDS elemental mapping of SnO₂ NP superlattices after 200 cycles, showing the preservation of ordered structure without NP aggregation. Scale bar, 50 nm.