Coaxial TiO2 carbon nanotube sponges as compressible anodes for lithium-ion batteries

Carbon nanotubes (CNTs) have been combined with TiO2 to improve its performance in applications such as lithium ion batteries; previous CNT/TiO2 hybrid structures were usually in the powder form which requires a polymeric binder and carbon black to make electrodes. Here, we fabricate freestanding bulk electrodes by depositing TiO2 onto a CNT sponge via a simple in situ hydrolysis method, creating coaxial units of TiO2-wrapped CNTs. The built-in CNT framework supports a uniform thin crystalline TiO2 forming a highly porous, conductive and compressible composite sponge. As an anode material for Li ion batteries, the TiO2-CNT sponges exhibit stable charging/discharging plateau voltages, excellent cycling stability and rate performance. In particular, these sponges can be compressed to much smaller volumes with significantly improved areal capacity, which cannot be achieved by powder-form electrodes. Our hierarchical sponges with optimized microstructures may serve as stable and compressible electrodes for various energy storage systems such as Li-ion, Na-ion and Li-S batteries.