Free-standing Hierarchical Porous Assemblies of Commercial TiO₂ Nanocrystals and Multi-walled Carbon Nanotubes as High-performance Anode Materials for Sodium Ion Batteries

Highlights: • Utilization of commercial nanomaterials to freestanding sodium electrode is demonstrated. • Free-standing electrodes composed of TiO₂ and MWCNTs are hierarchically porous. • Hierarchical porous architecture benefits charge transport and interfacial Na⁺ adsorption. • Free-standing hierarchical porous electrodes exhibit superior Na storage performance. - Abstract: Freestanding hierarchical porous assemblies of commercial TiO₂ nanocrystals and multi-wall carbon nanotubes (MWCNTs) as electrode materials for sodium ion batteries (SIBs) are prepared via modified vacuum filtration, free-drying and annealing. Microstructure characterizations reveal that TiO₂ nanocrystals are confined in hierarchically porous, highly electrically conductive and mechanically robust MWCNTs networks with cross-linking of thermally-treated bovine serum albumin. The hierarchical porous architecture not only enables rapid charge transportation and sufficient interaction between electrode and electrolyte, but also guarantees abundant interfacial sites for Na⁺ adsorption, which benefits substantial contribution from pseudocapacitive Na storage. When it is used directly as an anode for sodium-ion batteries, the prepared electrode delivers high specific capacity of 100 mA h g⁻¹ at a current density of 3000 mA g⁻¹, and 150 mA h g⁻¹ after 500 cycles at a current density of 500 mA g⁻¹. The low-cost TiO₂-based freestanding anode has large potential application in high-performance SIBs for portable, flexible and wearable electronics.