Protein-assisted assembly of mesoporous nanocrystals and carbon nanotubes for self-supporting high-performance sodium electrodes

Large-scale adoption of sodium-ion batteries in energy storage and conversion devices requires the development of electrode materials with high capacity, high-rate performance and long cycling life. Herein, a self-supporting electrode composed of mesoporous NaTi₂(PO₄)₃ nanocrystals and multi-wall carbon nanotubes for Na storage is described. The fabrication process involves protein-assisted self-assembly, a vacuum filtration process, and thermal treatment. The self-supporting electrode possesses favorable features such as hierarchical porosity, interconnected conductive networks, plenty of sites for intercalation-based and interfacial Na storage, and high mechanical robustness, as well as strong synergistic coupling between each constituent. The electrode used directly as the anode in sodium-ion batteries delivers excellent performance such as a high capacity of 132 mA h g⁻¹ at 1C, a high initial coulombic efficiency of 99%, and a high-rate capability of 62 mA h g⁻¹ at 50C, as well as long-term cycling stability with a capacity of 87% at 10C after 3000 cycles. The freestanding anode possesses favorable properties up to a thickness of 50 μm boding well for a high volumetric/areal capacity. Our study has great potential to be applicable to a wide range of mesoporous nanocrystals of both anodes and cathodes for high-performance energy storage and conversion devices.