Reevaluating carbonization: The untapped potential of pristine ZIFs for lithium metal batteries

Abstract

Zeolitic imidazolate frameworks (ZIFs), a subclass of metal organic frameworks (MOFs), have shown significant potential as hosts for lithium metal anodes due to their high surface area, tunable porosity, and thermal stability. Over the past few years, it has been widely assumed that carbonization of ZIF-based electrodes is essential for enhancing electrochemical performance by improving conductivity and structural integrity. However, this approach often overlooks the intrinsic properties of pristine ZIF structures. This study challenges this assumption by unveiling the untapped potential of pristine ZIF-8. Detailed electrochemical and kinetic analyses reveal that pristine ZIF-8 outperforms carbonized ZIF-8 (C-ZIF-8) in key areas such as lithium-ion diffusion and long-term cycling stability. While C-ZIF-8 exhibits uniform lithium nucleation and high performance at low current densities (less than 0.2 mA cm- 2), its performance declines at higher current densities due to limited lithium-ion diffusion. In contrast, pristine ZIF-8 demonstrates stable performance at high current densities (above 0.3 mA cm- 2) and prolonged cycling over 1600 h. Operando optical microscopy shows that lithium deposition occurs beneath the ZIF-8 layer, whereas surface deposition on C-ZIF-8 leads to dendritic growth. Additionally, ZIF-8 forms a Li3N-rich solid electrolyte interface, enhancing ionic conductivity and interfacial kinetics. These findings emphasize the limitations of carbonization and highlight pristine ZIF-8 as a more effective design strategy for lithium metal anodes. By leveraging its unique structural and functional attributes, pristine ZIF-8 effectively addresses challenges such as dendritic growth and solid electrolyte interface instability, offering a new paradigm for high-performance lithium metal batteries.