Self-assembled nanoflower zeolitic imidazolate framework-carbon for superior sodium storage

Abstract

Conventional hard carbon anodes, despite their high sodium storage capacity, suffer from two major limitations: sluggish ion diffusion kinetics due to tortuous micropore networks and significant volume expansion arising from disordered carbon structures. These inherent defects collectively compromise rate capability and cycling stability. Herein, we devise a graphene oxide (GO)-directed templating approach to architect zeolitic imidazolate framework (ZIF)-derived carbon into a hierarchical nanoflower superstructure with radially aligned meso/macroporous nanosheets. This superstructure integrates three synergistic features: three-dimensional interconnected channels and graphitic domains enabling fast ion/electron transport, radially aligned nanosheets maximizing electrode–electrolyte contact while accommodating volume expansion, and nitrogen-doped defect sites providing preferential redox-active centers for sodium storage. The optimized ZIF-9@GO-6 achieves a high specific capacity of 521.8 mAh·g−1 at 0.05 A·g−1 with an initial Coulombic efficiency of 89.2%, and retains a specific capacity of 298.2 mAh·g−1 after 500 cycles. This GO-directed morphological engineering strategy effectively resolves the intrinsic trade-offs between porosity, conductivity, and structural stability in conventional hard carbon anodes, paving the way for scalable, high-performance sodium-ion batteries.

1. Introduction

In the context of global carbon peaking and carbon neutrality goals, the development of sustainable green energy storage materials is progressing rapidly [1]. Sodium-ion batteries (SIBs) are regarded as a promising alternative to lithium-ion batteries (LIBs) due to their abundant resources, lower cost, and similar electrochemistry [2–4]. Hard carbon [5] stands out as a leading anode candidate for SIBs due to its high sodium storage capacity and low sodium insertion potential [6–7]. However, conventional hard carbon anodes are limited by their micropore-dominated and disordered pore structures, which result in slow Na+ diffusion kinetics, significant volume expansion, and uneven distribution of defect sites [8–11]. These limitations severely restrict the rate capability and cycle life of SIBs.

Recent advances demonstrate that zeolitic imidazolate frameworks (ZIFs)-derived carbon materials have made significant progress in the optimization of porous structures, owing to their high specific surface area (SBET), tunable pore structures, and abundant active sites [12–15]. Based on the strategy of nanoarchitectonics, researchers now precisely engineer ZIF-derived carbon microstructures by manipulating: (i) metal precursor composition, (ii) templating approaches, and (iii) controlled self-assembly pathways [16–21]. On the one hand, the introduction of multi-metal components (e.g., Zn, Co, Fe, and Ni) induces catalytic graphitization while simultaneously promoting meso/macropore formation via Ostwald ripening during pyrolysis [22–25]. This synergistic effect mitigates the overlap of electric double layers and enhances electron/ion transport kinetics. However, nanoparticle aggregation, spatial inhomogeneity, and inadequate size control frequently result in inconsistent graphitization and disordered porosity. On the other hand, the integration of hard templates, surfactant-derived soft templates, or polydopamine-mediated assembly enables the synthesis of hollow carbon spheres with hierarchical porosity, significantly enhancing electrolyte infiltration and mass transport kinetics. However, these strategies involve complex procedures, costly etching processes, and low yields, limiting their scalability [26–27].