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

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.