A MOF-modified NaCrO2 cathode for high-rate and wide-temperature applications in sodium-ion batteries

Abstract

Sodium-ion batteries (SIBs) are considered promising candidates for energy storage devices due to their abundant resources and low cost. In this study, Cr-based metal–organic frameworks (MOFs) are chosen to modify the NaCrO₂ cathode material during the synthesis process for achieving prominent electrochemical performances. The modified NaCrO₂ demonstrates significantly superior rate performance compared to pristine NaCrO₂; for instance, while pristine NaCrO₂ struggles to charge and discharge at 50C, the coated material retains a capacity of 72.9 mA h g⁻¹ even at this high rate. Even at an elevated temperature of 55 °C, the coated NaCrO₂ exhibits excellent cycling stability, retaining 85% of its initial capacity after 200 cycles at 0.5C, demonstrating its robust performance under challenging conditions. Comprehensive characterization, including Neutron Powder Diffraction (NPD), X-ray Absorption Spectroscopy (XAS), and in situ X-ray Diffraction (XRD), reveals that the Cr₂O₃–C coating on the surface of the NaCrO₂ cathode significantly enhances surface ionic transport while minimizing side reactions with the electrolyte by effectively isolating direct contact between the electrode and the electrolyte. The MOF-modified strategy improves cycling stability by suppressing interfacial side reactions and optimizing the phase transition process, while enhancing rate capability by facilitating ion transport. This work provides new insights for the design of high-rate, wide-temperature, and low-cost large-scale energy storage systems.